1996 Cherokee 4.0 Tune Up.

[streetxj]

Since I got the cherokee, the idle was a bit rough, especially when the engine was cold. The idle stays in the same rpm, so it doesn't fluctuate like if it had a bad IAC sensor. The exhaust even smelled like if did not have a cat (it does have one). Today or yesterday (sunday), when my dad and I took out the spark plugs, we noticed that they looked old, but they were burning good. When we checked the gap, all of them were .042 to .045 in gap! So we cleaned up the normal carbon build up on the plugs by using sand paper and gapped all of them to .035 like recommended. They are stock champion copper replacement plugs. We also replaced the fuel filter (still had the original one :roflmao and installed a new stock replacement cap and rotor from autozone. The spark plug wires are belden max power wires which are still in great shape. We also did an oil change. I used mobil 1 10w-30 high mileage oil with puralator pure one oil filter. It had very thin newish oil from when the previous owner got it serviced at jiffy lube. I noticed that my engine sounded like a diesel engine, so I got the feeling that the oil they put in wasn't too good. Now it runs much quieter. I can hear the fuel injectors over the rockers. Are noisy injectors normal?

Oil pressure is slightly above 40 when hot and almost on 80 when cold. Not bad for 158,700 miles. We also noticed that this engine shockingly has zero oil leaks. Everything under the engine looked dry. Overall, the engine runs better but still has that weird roughness to it, which goes away with usage, especially when the engine warms up. Again, it only happens under 1000 rpms. It basically sputters. At least the gas smell from exhaust went away. Today, I bought online champion stock replacement copper plugs, new upstream NTK oxygen sensor, coolant temp sensor and air charge temperature sensor. All of the sensors have never been changed. I'm not touching the post cat sensor cause it's just there to tell the ECU the condition of the cat. The upstream pre cat sensor is the one that controls the air/fuel ratio. Hopefully, the o2 and ACT sensor would fix the mild idle roughness it has. It's kinda like it has a mild cam in it.

Once I'm done with it, I'm going to reset the computer to clear any hidden codes it might have.

 

[yossarian19]

I had the same symptoms even after performing the same maintenance.
For me, it was a dirty coolant temperature sensor connector. Sprayed both the male and female connectors with contact cleaner, used a pick to remove gunk, old toothbrush, more cleaner & re connected it. Runs ever so much better at idle.
The computer takes information from the temp sensor to adjust air / fuel mixture. If the computer gets bad info, it makes bad choices. Like people.

 

[Dr. Dyno]

You could also try running some Seafoam through the engine to remove some of the carbon deposits from the combustion chambers.

 

[streetxj]

I had the same symptoms even after performing the same maintenance.
For me, it was a dirty coolant temperature sensor connector. Sprayed both the male and female connectors with contact cleaner, used a pick to remove gunk, old toothbrush, more cleaner & re connected it. Runs ever so much better at idle.
The computer takes information from the temp sensor to adjust air / fuel mixture. If the computer gets bad info, it makes bad choices. Like people.

It might just be that cause during the hottest part of the day in stop and go traffic, it seems to be almost on the white line right before the red overheat territory. The secondary electric fan still turns on and off though. The previous owner mentioned that he took it to the mechanic and the mechanic told him that the engine is running at a good temperature, that it was just the gauge that was reading too hot. I have a new coolant sensor that I bought anyways, but I'll clean the plug when I change it like you've mentioned. Thanks.

 

[streetxj]

You could also try running some Seafoam through the engine to remove some of the carbon deposits from the combustion chambers.

Thanks for the advice. I'm planning on doing that before changing the spark plugs and the o2 sensor.

 

[streetxj]

Well, that mechanic was full of $hit... Changed the clutch fan with a imperial thermal standard duty stock replacement and it moves MUCH more air. I noticed that the old fan clutch barely moved any air even when the engine was at a higher rpm. The lock-up feature wasn't operating correctly. I cleaned the contacts of the coolant sensor and it still sputters at idle, which mostly goes away when the engine is warmed up. Maybe the sensor itself is bad. I'm still going to seafoam it like dr. dyno recommended and replace the spark plug wires while I'm at it. They look good, but looks can be deceiving.

 

[bigalpha]

Clean your throttle body.

 

[streetxj]

^thanks. I just changed the spark plugs, the pre cat (upstream) o2 sensor, coolant temp sensor, and intake air charge temperature sensor and it runs much better now without any sputtering. Before I did any of this I ran sea foam. Well, there was zero smoke... I guess the valves and combustions chambers were very clean.